1. Field of Invention
The present invention relates to a sample positioning system, particularly to a method and system for scanning a laser beam on a workpiece to perform an automatic vertical positioning of the workpiece on the basis of a lateral movement pattern of the laser beam projected thereon.
2. Description of the Invention
In general, the technique for surface analysis, specifically an opto-acoustic film measurement, requires an accurate placement of the probed sample with respect to the instrument hardware. To achieve this, the measurement accuracy requires a precise positioning of the sample surface along the normal axis. Various types of laser pattern generation systems have been proposed using multiple laser beams that are optically modulated to perform the surface analysis of a particular workpiece. One way to detect such a pattern is to use a commercially known product, xe2x80x9coptoNCDTxe2x80x9d, made by MICRO-EPSILON(trademark) (a subsidiary of MICRO-EPSILON Messtechnik GmbH and Co. KG located in D-94493, Ortenburg, Germany).
Basically, there are two approaches to general surface analysis to find the optimal-signal position of the sample. One approach is based on signal optimization, and the other approach relies on some auxiliary optical focusing scheme. In the former approach, the sample position is continually scanned through the region and compared to an optimal reference point. Then, during operation, the sample position is corrected as the sample deviates from the optimal reference point. Here, the optimal reference point represents the desired sample position to obtain optimal performance in a particular process, such as a waffering process. Currently, the time response of the instrument to adjust back to the optimal point is long and impractical to implement. In comparison, the latter approach employs video imaging of some feature on the sample surface and adjusts the position of the sample based on the point of maximum contrast. However, this technique requires the availability of some feature with sharp edges on the sample, thus not applicable to flat surface samples, such as blanket metal films. Although the latter approach is usually faster than the former optimization method, the maximum contrast search still requires a time-consuming positioning delay while scanning the sample. In addition, other optical focusing techniques employing a special image created with a dedicated optical setup are required, adding costs and complicating the instrument design.
In summary, the conventional methods are slow in adjusting the position of a sample to coincide perfectly with an optimum-signal point. Moreover, very fine alignment and expensive measuring devices are required. Accordingly, there is a need for an efficient and economical mechanism that is capable of performing a rapid determination of the surface position, while providing active feedback control for signal optimization.
The present invention relates to a method and system that is capable of scanning a laser beam on a workpiece to perform an automatic vertical positioning of the workpiece in a particular manufacturing process.
Accordingly, the present invention provides a positioning system, which includes a light generating means for projecting a light beam onto the top surface of the workpiece at a predetermined angle and a video capturing means for detecting the light received by said workpiece for processing a deviation direction and a deviation amount based on the positional relationship between a digital image of the projected light on the surface of the workpiece and a predetermined reference image. The method of adjusting the vertical position of a workpiece is performed by the following steps: transmitting a light beam onto the top surface of the workpiece at a predetermined angle relative to a normal axis associated with the workpiece; detecting the light beam projected on the top surface of the workpiece; determining a center point of the detected light beam; determining a lateral distance between the center point of the detected light beam and a predetermined reference point; converting the determined lateral distance to a corresponding vertical distance using trigonometry; and, adjusting the vertical position of the workpiece based on the vertical distance outcome.